1. Field of the Invention
This invention relates to powder-form lubricant additives and to their use for water-based drilling fluids in the oil and mine drilling field.
2. Statement of Related Art
In the sinking of wells, particularly in the oil drilling field, the drilling fluids used nowadays have to satisfy stringent requirements. The drilling fluids, which for reasons of cost normally contain water as their main constituent, have to perform several functions at the same time, their overall quality being judged by whether they are capable of meeting an optimum of all requirements.
One of the most important functions of a drilling fluid is the removal of the so-called "rock cuttings" released by the bit, i.e. carrying the solid material detached to the surface. Drilling fluids having too low a viscosity are unable to remove the rock cuttings. Another, albeit not the most important requirement is the cooling and lubrication of the drill bit and drill pipe. However, this particular requirement is becoming increasingly important, particularly in the case of relatively deep walls, insofar as the drill pipe cannot always be guided "straight" due to the geological formations, instead so-called "crooked bores" are formed where the drill pipe comes into mechanical contact with the rock formation and wears relatively quickly at the high rotational speeds normally involved. Good lubrication by a suitable drilling fluid increases the life of the drill bit and the drill pipe. Economic advantages can be obtained not only by reducing wear, but also by eliminating the need to replace the drill bit and/or the drill pipe.
Drilling fluids differing widely in their composition have been used to satisfy the above-mentioned requirements. Thus, it was for some time standard practice to add mineral oil as a lubricating additive to drilling fluids in quantities of from 5 to 10% by weight. As a result, serious ground water pollution occurred so that mineral oils are no longer permitted as lubricating additives to drilling fluids. In addition, it has been proposed to use a tiglyceride/alcohol mixture to reduce torque in drilling fluids. However, this mixture does not have the desired lubricating effect and, in addition, causes troublesome foaming of the drilling fluid.
In addition, tall oil has been widely used in drilling fluids. It serves as an emulsifier in emulsion-type drilling fluids whether of the oil-in-water type or of the water-in-oil type. For example, U.S. Pat. No. 4,212,794 describes the use of a tall oil fraction of high resinic acid content as lubricant for aqueous drilling fluids, this tall oil fraction being said to have a fatty acid or oil content of at most 20%. Although it was possible in this way to achieve improved biological degradability and clearly to reduce the hitherto known troublesome foaming, these lubricants were unsatisfactory in their lubricating properties where highspeed drill bits were used and did not meet the demands made of them.
U.S. Pat. No. 3,810,836, U.S. Pat. No. 3,840,460 and U.S. Pat. No. 4,064,055 describe liquid drilling fluid additives consisting essentially of paraffins oils and sulfurized oils and of high molecular weight fatty acid esters as emulsifiers. U.S. Pat. No. 4,064,055 discloses an alkyl ester of an oxazolidine derivative as a further additive. Although such additives were satisfactory in regard to their cooling and lubricating properties for the drill bit and the drill pipe, they are attended by the serious disadvantage that they solidify at low temperatures due to their relatively high pour point and, as a result, are very difficult to dose and are equally difficult to introduce into the actual drilling fluid at low temperatures. This results in unwanted overdosage which involves economic disadvantages.